Sun makes slow light

The surface of the Sun puts on a spectacular light show as tiny granules of hot gas rise and fall in the sun's magnetised atmosphere, but underneath this bubbling cauldron the pace is much more relaxed. (Source: NASA)

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Last time, I talked about how the Sun, the source of practically all life on our planet, was pretty slack with its nuclear burning. It did so little of it, that (volume for volume) it put out about as much energy as a backyard compost pile, not a hydrogen bomb.

But what's this about the Sun making slow light? Let me put it in a different way. A photon of light takes only eight minutes to get to the Earth from the surface of the Sun. But it can take 100,000 years from the core of the Sun to get to the surface — where it bursts out and flies at the speed of light. What's going on?

Well, the density of the core is incredibly high — 150 times greater than water. So all the atoms are jammed up against each other.

Let's look at a pair of hydrogen atoms that have fused together to make a helium atom — and released a lot of energy, in the form of gamma rays. The gamma rays can travel only a few millimetres, before they're absorbed by an atom, and then re-radiated. Over and over again, they are absorbed, and then re-radiated. So, very slowly, the gamma-rays that have been generated by nuclear burning work their way up from the dense core.

After thousands upon thousands of years, they make their way into what's called the 'radiative zone'. The radiative zone is huge — it stretches up from the outer core (that's at the 24 per cent mark) to about 70 per cent of the way to the surface. It's called the radiative zone, because here, energy travels by radiation. The gamma rays are still being absorbed and re-radiated, but each time they're being re-radiated at longer wavelengths. They gradually get converted from gamma rays down to visible light. The temperature in the radiative zone is around 7 million°C near the bottom, and about 2 million°C near the top.

Above the radiative zone, in the top 30 per cent of the Sun's radius, is the convective zone. It's called the 'convective zone', because energy is convected, or carried by moving matter, just like rising water in the pot on the stove carries heat energy.

Let's look at a photon, many thousands of years after it was first made at the core of the Sun, as it enters the convective zone. The gamma ray photon heats the 'gas' in the convective zone. The gas is very hot, but not quite hot enough to re-radiate the energy. Instead the hot gas rises, and it carries the energy with it. It carries energy (as I said earlier) in the same way that water in a pot on the stove carries heat — with the hot stuff rising and coming to the surface, spreading out to the side, cooling, and then sinking again.

With the right telescope, you see 'boiling' patterns on the Sun's surface.

Deeper below the surface, there are giant 'cells' called 'supergranules'. They carry this hot gas towards the surface, then sideways, and then bring it down again. These supergranules are around 30,000 kilometres across (about 2.5 times bigger than the Earth), about 10,000 kilometres deep, and last for about two days. The hot gas moves up, across, and down fairly "slowly" — only about half a kilometre per second.

But just under the surface, the supergranules break down into little baby granules. Once again, in these granules, the gas rises, spreads sideways and then sinks like water in your bubbling pot — but at around 2 kilometres per second. Granules are about 1,000 kilometres in diameter, and there are millions and millions of them covering the surface of the Sun. They're around 300 kilometres deep. These granules live for about an average of eight to 20 minutes. The granules are hotter in the centre, and cooler at the edges, but the average temperature at the surface is around 5,500°C.

The photons of energy have finally, after 100,000 years, come to the end of their journey inside the Sun. They have now reached a zone which is transparent to light. The photons escape into space, and travel at the classic speed of light — around 300,000 kilometres per second. The very surface of the Sun is called the 'photosphere', because that's where the photons have escaped from.

So while in eight minutes, a photon of light can travel the 150 million kilometres from the Sun to the Earth, in that same time, a gamma ray in the Sun's core will travel only about 13 centimetres. That's a pretty slow rate of delivery.

For all its flashy show on the surface, deep down the Sun would seem to be kind of lazy…

Gerhard :

Harry :

27 Apr 2012 12:58:13pm

Saying "a photon can take 100,000 years from the core of the Sun to get to the surface" and "in eight minutes ... a gamma ray in the Sun's core will travel only about 13 centimetres" implies that it is the same photon doing the travelling. I'm wondering whether photons would lose their identity during the cycle of re-absorption and emission.

Urien Rakarth :

28 Apr 2012 9:09:54am

It shouldn't do, Harry. Unless you mean its identity being defnined by its wavelength. A photon is a unit of energy (quantum of light) and carrier of the electromagnetic force. Nor can it be destroyed.

drkarl :

29 Apr 2012 10:13:09am

Same photon travelling from core of Sun to surface? Actually, you are correct. It is not the same photon. Indeed, one gamma photon turns into many many optical light photons. Sorry for the clumsy writing. Karl

Psychaotix :

28 Apr 2012 12:44:41am

Certainly seems lazy to me, a fact which I'm grateful for!

Oh, and Garrett, the Sun uses Nuclear Fusion (not fission, which is what our nuclear plants here on earth use) to generate it's power. It's renewable in the contect that it won't be exhausted in the lifetime of you, or even your great great great grandkids, but ultimately it'll run out of hydrogen. After that, well, it's pretty much game over.

jim :

14 May 2012 12:54:14am

Very interesting.On the theory that the surface of the sun is a field. Could the Sun be permanently recycling to extents like the solar/ hydrogen and return production cycle using solar to make hydrogen then back to water?Some people say that the sun looks hollow because of viewing the black areas that appear on the surface and seem to be windows to inside.Creating what appears to be a field as the Suns surface with a hollow interior.Perhaps while the Sun can concentrate and feed on dark matter and energy in an existing time exchange it will have extended life but eventually the imbalanced exchange rate of matter and spacetime demands may take it's toll and we find ourselves living on the edge of a black hole.

As the universe expands and calls on sympathies and matter behind in space time to give way like suction down pathways to the universe front lines, we may find that Sun's are a precursor and visible event supporting the action of expansion forces not so much just local chance. Especially those with a solar system. Which may be an indicator that ours is an action of negative energy opposite to what's going on in centre galaxy. An opposite effect.Unless our solar system is part of black hole existing structure.

Time change may be achieved by recording clocked time approaching an event horizon.

To every action... Such an action of universe expanding and time and matter vacuum as stretched-worm holes- moving to the front of the expansion and in some cases to rear, would have to have an equal and opposite reaction which may be drag to the expansion which would give time.

Worm holes may go both ways.Perhaps matter is the drag and balance on expanding space time.This may indicate why our solar system has no bow wave but will have some exchange going on where it meets space. Eventually the rim of an event horizon.Without all the strains we are nothing.This theory indicates our Sun and solar system to perhaps be a forming branch of our centre galaxy black hole or a sympathy to time or space vacuum to somewhere else in our own galaxy by scale and spiral galaxy forces. Or drag on the centre action.Eventually being pulled through time to expansion sympathies like in a water whirlpool going down a drain unless the sympathy force stops by a satisfied action or somehow countered. Our solar system may be sympathetic to outer and other, not centre black hole galaxy spiral sympathies of time and matter displacements and vacuums.

If our so expected flat universe has no poles, the playing field gets complicated and less predictable. But may not exist otherwise.Rotation and poles on our universe may indicate forces of other universes.The galaxy formations inside it and other mechanics may be indicative of this.Of greater universe and outside rules.Anyway, I think our Sun is already under movements to time sympathies of displacements or universe expa

jim :

15 May 2012 12:52:24am

A lot easier to draw than to say.

I can't see worm holes existing that can be traversed. If the black holes are the "ends of veins" being drawn to the front or filling gaps of universe expansion or by forces that would exist to opposite in retaliation, there doesn't appear to be visually, yet, any evidence of abilities for man to traverse a worm hole.

Minute recordings of time counters, frames, entering an event horizon may be a way of measuring any time distortion at an event horizon. Filming a star disappearing down a hole would be a bonus but would have to be recorded so the 'frames " could be applied by milliseconds to view to discern any light/time abnormalities or distortions.

If the sun and solar system are a birthing black hole or similar scale and relation to the action,or an embryonic on a vein too small to event,the tube break, we may have the structure to view the mechanics of a black hole and time with more information on the sun.I believe negative energy is in the process and matters of time already. In the sun.Like an ember perhaps to describe better, waiting to burn through the space time blanket. Drawn,vacuum'd, instigated by the expanding universe and need for dark matter and energy.What goes into a black hole may come out as the elusive sub atomic matter needed to knit with the time blanket- dark energy, for expansion or filling gaps. Eventually that matter and energy accumulates to gas and dust in cases as our sun and planets were formed.

Red dwarf or sun to be red giant etc dependant on composition, circumstances of chance and position.

Our sun more interactive with time ,the space time blanket, than a red dwarf. The matter may depend on negative energy plus original composition of course.